Hi! I'm working on an hydroponic system. Thoug I know Irricad is not conceived for this, I'm using it to calculate the diameters of main water supply lines. The arrangement consist on 122 flexible tubes (internal diameter 4mm) connected along a single PVC line, the separation between tubes is 3''. The pressure drop between the first and the last one must be near zero to achieve uniformity (since there is no control on the flow apart from the flexible tubes).
I measured the flow trought the flexible tube at different pressures, and with that info I entered it as an emiter and nozzle.
Now the poblem is, that the numbers of pressure drop I get from Irricad are an order of magnitud above the ones I get calculating the pressure drop with another software. Why can that be? Can the small space between emitters (3'') be affectig the calculations? how can I get more precisse calculations?
I did this same thing with other emitters, and keep getting wrong numbers.
Thank you in advance.
Regards,
Pressure drop doesn't match manual calculation.
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jovivier
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Re: Pressure drop doesn't match manual calculation.
Hi,
It is difficult to comment without seeing the design.
Did you draw the pipe as a connected sprayline or as pipe and outlets (unconnected sprayline)?
The first possible causes that come to mind are:-
- Check the emitter constant and index - do these provide the correct flow at the specified pressure?
- Turn off minor losses in Design|Zone Design Configuration. This is the calculation of the headloss at each connection to the pipe. This will be lower in connected spraylines.
If the emitter flows are quite low it might be better to mirror this as a tape rather than a sprayline.
In general for hydroponics, or any outlets above ground level, the outlets require an outlet connector with the correct "height above ground". Without an outlet connector the emitters will be assumed to be at ground level. If you have used an outlet connector then check the Zone Full Report in the "Outlets and Inflows" section for a higher-than-expected "Out Loss". This is the headoss through the outlet connector. Because the database dialog for outlet connectors requires data in both metres/feet and mm/in it is easy to enter the wrong value and end up with a high headloss.
If you are still unable to find the cause please feel free to email your design and database to your local support team or ourselves (Support@IRRICAD.com).
The IRRICAD Team
It is difficult to comment without seeing the design.
Did you draw the pipe as a connected sprayline or as pipe and outlets (unconnected sprayline)?
The first possible causes that come to mind are:-
- Check the emitter constant and index - do these provide the correct flow at the specified pressure?
- Turn off minor losses in Design|Zone Design Configuration. This is the calculation of the headloss at each connection to the pipe. This will be lower in connected spraylines.
If the emitter flows are quite low it might be better to mirror this as a tape rather than a sprayline.
In general for hydroponics, or any outlets above ground level, the outlets require an outlet connector with the correct "height above ground". Without an outlet connector the emitters will be assumed to be at ground level. If you have used an outlet connector then check the Zone Full Report in the "Outlets and Inflows" section for a higher-than-expected "Out Loss". This is the headoss through the outlet connector. Because the database dialog for outlet connectors requires data in both metres/feet and mm/in it is easy to enter the wrong value and end up with a high headloss.
If you are still unable to find the cause please feel free to email your design and database to your local support team or ourselves (Support@IRRICAD.com).
The IRRICAD Team
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facun.s
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Re: Pressure drop doesn't match manual calculation.
Hi! thank you so much for your answer. The problem was in the minor loss calculations. I deactivated that option for the zone, and the numbers got perfect. The head loss changed from 1,42m to 0,03m. ¿Can I have some insight about how the minor losses are calculated? ¿How come they are so high on this particular case? ¿Is there a coefficient that I can mange to get more accurate ressults?
I'm sending you the design and database by email in case you want to check it out.
PS, I just saw you're based on Blenheim, I spent some time of a working Holiday doing some pruning there. Love your city, an big love to NZ!
Regards,
I'm sending you the design and database by email in case you want to check it out.
PS, I just saw you're based on Blenheim, I spent some time of a working Holiday doing some pruning there. Love your city, an big love to NZ!
Regards,
-
jovivier
- Site Admin
- Posts: 919
- Joined: Thu Mar 12, 2009 2:57 pm
- Company: Lincoln Agritech Ltd, IRRICAD Software
- City / Town: Lincoln
- Location: Canterbury, New Zealand
- Contact:
Re: Pressure drop doesn't match manual calculation.
Hi,
As per the Help|Help Topics - User Manual -> Advanced Topics -> Spraylines, Tapes and Minor Losses:-
Minor Losses Explained
Minor losses are the headlosses associated with fittings i.e. size changes, crosses, tees, elbows, take-offs etc. IRRICAD accounts for minor losses with a conservative equivalent length method, an extra length is assigned to each pipe segment to allow for the headloss.
Spraylines and Sprayline Blocks
Losses down a submain (allowing for LTO or losses through Tees/Crosses), in blocks of connected or unconnected spraylines, are calculated using the minor loss method.
For connected spraylines minor losses, to account for barb losses at the emitter/riser connections, are calculated in a similar manner, however the loss assigned in a connected sprayline is 50% of the loss assigned in an unconnected sprayline.
The allowance for minor losses (in pipes and connected spraylines) may be disabled in Zone Design Configuration. This will effect both submains and laterals in sprayline blocks.
Tapes and Tape Blocks
LTO Losses down submains in Tape blocks are assumed to be negligible. Barb losses for tapes are calculated directly using the Kd specified in database.
The IRRICAD Team.
PS, I'm no longer based in Blenheim but now live in the Bay of Plenty - another nice spot in New Zealand
As per the Help|Help Topics - User Manual -> Advanced Topics -> Spraylines, Tapes and Minor Losses:-
Minor Losses Explained
Minor losses are the headlosses associated with fittings i.e. size changes, crosses, tees, elbows, take-offs etc. IRRICAD accounts for minor losses with a conservative equivalent length method, an extra length is assigned to each pipe segment to allow for the headloss.
Spraylines and Sprayline Blocks
Losses down a submain (allowing for LTO or losses through Tees/Crosses), in blocks of connected or unconnected spraylines, are calculated using the minor loss method.
For connected spraylines minor losses, to account for barb losses at the emitter/riser connections, are calculated in a similar manner, however the loss assigned in a connected sprayline is 50% of the loss assigned in an unconnected sprayline.
The allowance for minor losses (in pipes and connected spraylines) may be disabled in Zone Design Configuration. This will effect both submains and laterals in sprayline blocks.
Tapes and Tape Blocks
LTO Losses down submains in Tape blocks are assumed to be negligible. Barb losses for tapes are calculated directly using the Kd specified in database.
The IRRICAD Team.
PS, I'm no longer based in Blenheim but now live in the Bay of Plenty - another nice spot in New Zealand